A proton exchange membrane (PEM) fuel cell converts the chemical energy of fuels and oxidants directly into electrical energy. PEM fuel cells offer many advantages over conventional means of generating electrical energy. For example: they operate at relatively low temperatures and therefore require little or no warmup time; they are clean (their exhaust is typically water and air); they are efficient; and the typical sources of fuel/oxidant (hydrogen, air/oxygen) are in abundant supply.
The centerpiece of a typical PEM-type fuel cell is a solid polymer electrolyte (the PEM) that permits the passage of protons (i.e., H.sup.+ ions) from the anode side of the fuel cell to the cathode side of the fuel cell while preventing passage therethrough of reactant fluids (e.g., hydrogen and air/oxygen gases).
FIG. 1 depicts a conventional PEM-type fuel cell. A reaction on the anode side of the PEM produces protons (H.sup.+) and electrons. The protons pass through the membrane to the cathode side, while the electrons travel to the cathode side of the membrane through an external electrical conductor. On the cathode side, the protons and electrons react with oxygen gas to produce water. The external electron flow from the anode to the cathode is the electrical energy created by the fuel cell reaction that can be used to supply electricity to a load.
More specifically, as depicted in FIG. 1, the PEM fuel cell 100 comprises an anode-side fluid flow plate 102 for the flow of hydrogen, an anode area 104, a proton exchange membrane 106, a cathode area 108, and a cathode-side fluid flow plate 110 for the flow of oxygen or air containing oxygen. Areas 104 and 108 conventionally include a gas diffusion means (not shown). Hydrogen gas introduced from a hydrogen manifold 112 at the anode-side fluid flow plate 102 travels along a fluid flow channel 124 in the anode-side flow plate 102, and also diffuses in a direction perpendicular to the flow channel towards the anode area 104. In the anode area 104, the hydrogen gas is oxidized to form hydrogen nuclei (H.sup.+ ions or protons) and electrons. The H.sup.+ ions travel through the proton exchange membrane 106 to the cathode area 108, but the hydrogen gas itself does not penetrate the proton exchange membrane 106.
The electrons formed by the above-mentioned reaction are conducted from the anode area 104 to the anode-side fluid flow plate 102, to conductive collector plate(s) 114. Electrons flow from the collector plate(s) 114 through an external electrical conductor 116 to a load 118, and from the load to the cathode side of the fuel cell. At the cathode side, oxygen gas, either in pure form or as a component of air, is introduced to a channel 120 on a cathode-side fluid flow plate 110 from an oxygen manifold 122. The oxygen reacts with the protons (H.sup.+) coming through the membrane 106, and the electrons coming from the external conductor, to form water.
In the PEM cell, the two chemical reactions are: EQU H.sub.2 2.fwdarw.H.sup.+ +2e.sup.- (anode-side),
and EQU O.sub.2 +4H.sup.+ +4e.sup.- .fwdarw.2H.sub.2 O (cathode-side).
Each fuel cell typically delivers a relatively small voltage, on the order of 0.4 to 0.9 volts. In order to achieve higher voltage, fuel cells are often disposed as multiple layers connected in series within a fuel cell stack (described further herein).
Increasingly, PEM fuel cell research activity is concentrating on ever smaller stacks (for example, 1-5 kW). However, there is a parallel need to maintain high stack voltage, to provide higher electrical power conditioning efficiency, while continuing to reduce stack costs (for example, by minimizing the number of plates and joints within the stack). To meet these conflicting needs, new fluid flow plate and fuel cell stack designs are required.